Communication networks provide many people and organizations with access to a variety of applications and services. A typical communication network employs a layered communication and protocol design in which each layer represents a collection of conceptually similar functions. The layers are arranged hierarchically, with each layer typically providing services to the layer above it and requesting services from the layer below it.
As an example, a typical layered design of a communication network patterned after the Open Systems Interconnection (“OSI”) reference model includes a physical layer, data link layer, network layer, transport layer, session layer, presentation layer, and application layer arranged hierarchically. The physical layer, data link layer, and network layer are commonly referred to as “media layers,” and the other four layers are commonly referred to as “host layers.”
The physical layer includes functions concerned with interactions between network devices and a physical medium. The data link layer includes functions concerned with transfer of data traffic across physical links interconnecting network entities. The network layer includes functions for end-to-end routing (e.g., source to destination) of data traffic. Typically, the data link layer receives and responds to service requests from the network layer by issuing service requests to the physical layer for transport of data frames across physical links.
Conventionally, the data link layer is not concerned with path detection, data traffic routing, error control, quality-of-service, and other “intelligence-type” functions that are left to the network layer. To illustrate, a data link layer switch device such as a conventional Ethernet switch device typically receives a service request from the network layer and simply forwards data traffic frames associated with the request to a port that has been mapped to a destination address, such as a Media Access Control (“MAC”) address, indicated in the service request. The port provides a connection to a physical link connecting the Ethernet switch device to another Ethernet switch device associated with the MAC address.
While the simple data traffic forwarding functionality of a data link layer device such as a conventional Ethernet switch device is well-suited for certain types of communication networks such as a small-scale local area network, it is problematic for other types of communication networks. For example, traditional Ethernet switch devices and protocols tend to cause congestion in optical transport networks and particularly in hybrid data link layer and optical transport network configurations. The congestion may be especially problematic when such hybrid configurations are used to transport significant loads of data traffic over large-capacity physical links and/or large geographic areas such as may be used in a backhaul network and/or a wide area network (e.g., a metro area network). To illustrate, a traditional Ethernet switch device is designed to maximize throughput over a physical link connecting two network devices. Accordingly, the Ethernet switch device will blindly forward data traffic frames over the physical link without considering the congestion, cost, or latencies associated with the link.
While the network layer is typically configured to perform path detection, data traffic routing, error control, quality-of-service (“QOS”), and other “intelligence-type” functions, such functions at the network layer do not always prevent congestion of physical links interconnecting network devices. Moreover, overhead associated with the network layer is significantly more than overhead associated with the data link layer. Thus, there is a need to optimize data traffic forwarding at the data link layer in communication networks such as optical transport networks.